The invention relates to a system for controlling the working conditions for mechanical pumps supplying associated devices with pressure fluid via a pipe system Further, the invention relates to a regulating valve for use in such a system.
When mechanical pumps are used for transporting a liquid, it is important to use regulating valves taking into account the characteristic of the pumps as well as of the devices served by the pumps. Especially for pumps having a large output it is important that the pumps in the starting phase get a counterpressure preventing them from xe2x80x9ccavitating outxe2x80x9d.
A typical system of the current type is a fire water system on an offshore installation. Such a system normally will comprise a very large pipe system having large variations in static and dynamic pressure. There will be a need for a number of regulating valves which are able to control the supply of water to the different sections in the installation. A typical size of regulating valves of the current type is from 4xe2x80x3 to 12xe2x80x3. Maximum through-flow will correspond to 10-20 m3/s liquid flow into the valves. The total pump output for the liquid flowing in the system may be up to 8000 kW.
The object of the invention is to provide a system of the current type which is provided with one or more valve devices ensuring satisfactory working conditions for all types of pumps transporting gas or liquid in the system.
The above-mentioned object is achieved with a system of the introductorily stated type which, according to the invention, is characterised in that a valve means is placed between at least one of the pumps and an appurtenant device supplied by the pump, which means is arranged to open only when the pump has started up, and by adjustment of its flow cross-section seeks to maintain its downstream pressure at a value which is predetermined from the specifications of the pipe system and said device, but gives priority to restrict its flow cross-section so that the counterpressure of the pump does not fall below a given minimum value determined from the characteristic properties of the pump.
According to the invention there is also provided a regulation valve comprising a housing having a through passage for through-flow of a fluid via an inlet having an upstream pressure and via an outlet having a downstream pressure, a main valve body defining the flow cross-section of the passage in cooperation with a valve seat, and a servo chamber communicating with a control valve means for influencing the movement of the main valve body, which regulating valve is characterised in that the main valve body has an end surface constituting a movable surface in the servo chamber, the servo chamber being so dimensioned in relation to the sealing surface of the valve seat that the main valve body gets a net force surplus to be moved towards the seat when the pressure of the servo chamber is increased up towards the upstream pressure of the valve, and that the control valve means comprises a first and a second control valve which, under the influence of the upstream pressure and the downstream is pressure, respectively, is arranged to regulate the volume of the servo chamber so that the main valve body is moved towards an increased flow cross-section if the upstream pressure exceeds a preset minimum value and the downstream pressure simultaneously is lower than a preset value.
By means of the invention there is provided a purely mechanical regulating valve monitoring both its upstream pressure and its downstream pressure simultaneously, and which is arranged to regulate in such a manner that the superior functional requirements for the entire pipe system are complied with. As a result of the fact that the regulating valve has such properties, the mechanical stresses on pumps, pipe system etc. will be able to be considerably reduced. Another important advantage is that the pump capacity can be utilised in a better manner in that the valve parameters are preset from the placing of the regulating valve in the pipe system. One is then let off from mounting throttling discs etc. to compensate for hydrostatic variations or a change in pipe dimensions etc. This will in turn make it possible to utilise the liquid supply capacity optimally and simultaneously save energy.